Oscillatory signal system with turn on and turn off rate control

ABSTRACT

A full scale oscillatory signal is multiplied by a ramp-type amplitude controlled rate signal to provide an output signal increasing linearly from zero volts to a full scale peak-to-peak value and then decreasing linearly back to zero. The rise portion of the ramp signal provides a controlled turn on rate for an oscillatory program command for material testing apparatus to avoid destruction of the specimen being tested, and the fall portion of the ramp signal provides a controlled turn off rate. Multi-channel test systems can be similarly controlled, only a single potentiometer being required for controlling the amplitude of all channels simultaneously.

I nited States 1 1 51, 4 Gross Aug. 14, 1973 OSCILLATORY SIGNAL SYSTEMWITH Primary Examiner-Richard C. Queisser TURN ON AND TURN OFF RATECONTROL Assistant ExaminerArthur E. Korkosz Attorney-Bugger, Peterson,Johnson & Westman Inventor: Alan E. Gross, Minnetonka, Minn. [73]Assignee: MTS Systems Corporation,

Minneapolis, Minn. [57] ABSTRACT [22] Filed; Jam 18, 1971 A full scaleoscillatory signal is multiplied hy a ramptype amplitude controlled ratesignal to provide an out- PP 107,343 put signal increasing linearly fromzero volts to a full scale peak-to-peak value and then decreasinglinearly 52 us. Cl. 73/673, 73/7l.6, 73/90, h The rise Signal 328/160vldes a controlled turn on rate for an oscillatory pro- [51] Int. Cl.G01n 3/32 gram cofnmand for mafierial tesling apparatus to avoid 5s 1Field of Search 73/673, 71.6, deshhchoh P F helhg tested and the307/229; 318/611; 328/160 163, 164 portion of the ramp signal provldes acontrolled turn off rate. Multi-channel test systems can be similarly[56] References Cited controlled, only a single potentiometer beingrequired UNITED STATES PATENTS for colntrollmg the amplitude of allchannels simultaneous 3,516,413 6/l970 McDonald et al. 328/160 y 26Claims, 4 Drawing Figures 12 FUNCTION P 10 GENERATOR 28b SPECIMEN LORD52 30 32 34 60 520 280 7 2o CELLS I SERVOVALVE 18 MULT|. I VALVE l v PLI E R i 28 AM P 16 w i s 5% S EFV6VT\LVE 22 54 [CONTROLLERS 30 54 F 1ACTUATOR *1 ACTUATOR "2 58 r MULTI- i VALVE Pl.lER I AMP FUNCTION 54b JGENERATOR 26 23b +10VDC ZERO CROSSING COMPARATOR WWW 3.151 .994

SHEET 1 022 6 12 FUNCTION /5 Hg 1 GENERATOR 2 28b SPECIMEN LOAD 60 520 i280 CELLS H 1 SERVOVALVE 1 MULTI- I E PLIER AMP 62 T l 28 y 16 22 14 52bSERVOVALVE 54 CONTROLLERS 30 64 i i 5 I ACTUATOR 1 ACTUATOR 2 3 F): g NFUNCTION J GENERATOR fl +1ov0c AMPLITUDE 120 v+ 123 COMPARATOR INVENTOR.AMA/v 5. 620 5'5 Attorneys OSCILLATORY SIGNAL SYSTEM WITH TURN ON ANDTURN OFF RATE CONTROL 1 BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to a system for turning onand turning off an oscillatory signal at controlled rates, and pertainsmore particularly to turning on and off an oscillatory program commandsupplied to material test apparatus.

2. Description of the Prior Art Vibration apparatus for determining thephysical characteristics of a specimen, particularly the fatigueproperties thereof, have been extensively used. The test specimen isplaced in the apparatus and then vibrated artificially to produce themechanical stresses and strains. Frequently, the oscillatory commandsignal is generated by a magnetic tape recorder. The shock developedfrom the sudden application of such an oscillatory signal at its fullpeak-to-peak value is acute, even causingdestruction of the specimen inmany instances. Previous attempts have used non-linear rates, which havebeen unpredictable as to the number of cycles required to obtain anaccurate full scale or 100 percent peak-to-peak amplitude.

SUMMARY OF THE INVENTION Accordingly, one general object of the presentinvention is to provide a system that will g gntrol the oscillatorysignal so that the full mnant??? flatmates. fl

55ft}: an aimfi'fiii n ve tion is to provide a system for controllingboth the turn on and turn off rates of an oscillatory signal that wouldotherwise be of sufficient magnitude to cause damage to the specimen tobe tested.

Another object of the invention is to provide controlled turn on andturn off rates for an oscillatory signal with the turn off rate beingfaster than the turn on rate. While the invention will have especialutility in conjunction with vibration testing apparatus, it is envisagedthat it may be found useful in other environmental situations.

Another object of the invention is to provide an amplitude control, sothat the full scale value or magnitude of the oscillatory signal may bereduced when circumstances so dictate. In other words, if theoscillatory command signal is recorded at a given strength, the strengthor value may be reduced when practicing the teachings of my invention.In this regard, an aim of the invention is to employ a singlepotentiometer which will serve to control the amplitude of a pluralityof channels whether or not they are all subjected to an identicalcommand signal or different command signals.

Yet another object is to provide circuitry of the foregoing character inwhich an integrator is utilized but which integrator does not hold thestatic level. Therefore, an aim of the invention is to obviate theadverse effect that integrator drift would cause. Stated somewhatdifferently, the integrator is used only during the turn on and turn offperiods, being switched out of the circuit during the remainder of thetime. Consequently, a further desideratum is to eliminate contactbounce, that is switching transients, when operating the Run- Stopcontacts which would normally occur with mechanical switches.

Still further, an object of the invention is to provide a dynamiccommand that once the turn on period has been passed it will furnish anaccurate peak-to-peak control. An aim of the invention in this regard isto provide a smooth transition from the rarnping or turn on portion ofthe cycle to an accurate static level which is utiligedduringthe.actuaitestingfifiihifiiiimfia A still further object of theinvention is to provide a control system of the foregoing character thatwill be quite simple and inexpensive to produce, yet highly reliable andlong lasting in its operation. Therefore, the use of my system will bewidely encouraged, both for utilization in vibration testing and also inother types of situations.

Briefly, the output from a direct current integrator is clamped at acertain negative voltage. When the Run- Stop contacts are operated tochange one from a normally closed position to an open position and theother from a normally open position to a closed position the integratorchanges polarity and the output therefrom starts to ramp with a positiveslope. When the output of the integrator equals zero volts, the outputof a zero crossing comparator changes its polarity state with the resultthat one field effect transistor is switched out and a second suchtransistor switched in. Although the integrator provides the amplitudecontrolled rate signal, which enables the dynamic command signal toreach its full scale magnitude, the rate at which this signal changes isinfluenced by the switching action. A third field effect transistor isthen switched in and the second one switched out, so that the amplitudecontrolled rate signal equals whatever value the master amplitudecontrol provides. By multiplying the amplitude controlled rate signal bythe full scale oscillatory signal, the result ing or product signal isincreased in magnitude during th upward ramping or rise portion of theamplitude controlled rate signal. The switching action, basicallyspeaking, is reversed during the turn off period, this being after thetesting operation has been completed.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a combined block andschematic diagram illustrating my control system when used withvibration testing apparatus;

FIG. 2 shows a typical oscillatory command signal for the testingapparatus of FIG. 1 without turn on and turn off rate modification;

FIG. 3 shows a ramp-type amplitude controlled rate signal for graduallyincreasing and later decreasing the peak-to-peak value of the signaldepicted in FIG. 2, and

FIG. 4 shows the resulting output signal derived from a multiplicationof the signals of FIGS. 2 and 3, the peak-to-peak magnitude increasingduring the turn on period and decreasing during the turn off period.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to FIG. I,exemplary vibration testing apparatus has been designated generally bythe reference numeral 10. A specimen 12 has been shown and constituteswhatever'i'fe'r'n is t d be subjected to vibrations so that itsproperties can be ascertained. For instance, it might be an a it plgrie; The illustrative testing a wt ifs Tfi i s supported on a rigidbody or floor 14. Actually, the apparatus 10 comprises two actuators I6and 18 in the present instance, the actuator I6 applying vibratorystresses to one portion and the actuator 18 to a second or spacedportion. The actuator 16 has a servovalve 20 associated therewith, andthe second actuator 18 has a similar servovalve 22 associated therewith.Supplying fluid to the servovalve 20 is a controller 24 and supplyingfluid to the servovalve 22 is a controller 26. Each controller 24, 26includes a summing junction or comparator 28 having inputs 28a and 28bplus an output 28c. As is typical, a valve amplifier 30 is also includedin each of the controllers 24 and 26, the valve amplifier functioning tomerely amplify the error or output signal appearing at the output 28c ineach instance. By means of load cells 32 and 34, there is a feedback tothe input 28b of each comparator 28. The actual oscillatory commandsignal is introduced into the controllers 24, 26 via the inputs 28a. Itshould be appreciated at this stage of the description that the signalintroduced at the inputs 28a of the controllers 24, 26 is the signalthat must be moderated or reduced in amplitude during the turn on andturn off period as will become better understood from the descriptionpresently to be given with respect to my control system.

It is felt that the above description of the testing apparatus 10 ismore than adequate for an understanding of one practical applicationwhere my invention will be of benefit. However, if further details aredesired, reference may be made to US. Pat. No. 3,442,120 titled ServoValve Controlled Hydraulic Resonant Machine," granted on May 6, 1969 toMax Russenberger et al.

The oscillatory signal system has been indicated generally by thereference numeral 50. inasmuch as two actuators 16 and 18 have beenillustrated, this serves as a basis for utilizing two control channels.Consequently, the system 50 in its exemplified form includes a pair ofmultipliers 52 and 54. Multipliers found satisfactory in actual practiceare manufactured by Motorola Semiconductor Products Inc. and carry modeldesignation MC 1595. For the sake of a simplified description of thesystem 50, the two inputs belonging to the multiplier 52 have been givenreference numerals 52a and 52b, the output of this particular multipliercarrying reference numeral 520. By the same token, the multiplier 54 hasa pair of inputs 54a and 54b plus an output 54c. It will be appreciatedthat whatever signals are delivered to the two inputs of eithermultiplier will be multiplied together andthe product thereof willappear as an output signal at the output 52c or 54c, as the case may be.

inasmuch as the apparatus 10 requires a twochanneled command, theoscillatory program signals are supplied by two function generators 56and 58. These generators 56 and 58 may be magnetic tape recorders orsuitable oscillators. in order to provide versatility to the testingprocedure, the function generators 56 and 58 can be connected so as tosupply signals to either the testing machine 16 or 18. To impart thisflexibility to the system, a trio of switches 60, 62 and 64 areemployed. When the switches 60 and 64 are closed, the switch 62 thenbeing open, it can be seen from FIG. 1 that the function generator 56 isconnected directly to the input 52a of the multiplier 52, whereas thefunction generator 58 is connected directly to the input 540 of themultiplier 54. On the other hand, when the switch 64 is open, and theswitches 60, 62 closed, then the function generator 56 is connected toboth inputs 52a and 54b.

Also included in the system 50 is what will be termed amplitudecontrolled rate circuitry 66. Before describing in detail the circuitry66, however, it will be well to refer to certain wave forms. In thisregard, attention is first directed to the oscillatory signal 68supplied by either the function generator 56 or the function generator58. FIG. 2 is a graphical representation of this wave form, and it willbe noted that the peak-to-peak amplitude is constant. It is thispeak-to-peak value that can be injurious to the specimen l2, and thepurpose of the present invention is to control the rate of turn on andalso turn off. The amplitude controlled rate signal 70 is pictured inFIG. 3. This is a ramp-type signal and is composed of certain portionsthat will be dealt with in detail hereinafter. The resulting outputsignal 72 which reflects the controlled rate as far as the turn on andturn off periods are concerned is set forth in FIG. 4. Portions of thissignal will be referred to in greater detail hereinafter.

At this time, the amplitude controlled rate circuitry 66 will bedescribed. It will be observed that a set or normally closed contacts 74are included and also a set of normally open contacts 76. These contacts74, 76 are interlocked by means ofa toggle mechanism 78 pictured only inphantom outline. It will be understood that when the toggle mechanism 76is actuated so as to open the normally closed contacts 74, then thenormally open contacts 76 will be at that time closed. Morespecifically, the contacts 74, 76 constitute Run- Stop contacts and therole performed by these contacts will become clear as the descriptionprogresses.

Attention is called to a positive supply voltage V*, which in practicehas been plus 16 VDC, and a negative supply of voltage V, which may beminus 16 VDC. One end of a resistor 80 is connected to the supply V andthe other end directly to the normally closed contacts 74. A secondresistor 82 has one end connected to the negative supply voltage V andits other end to the normally open contacts 76. The common or joinedsides of the contacts 74 and 76 are connected through a potentiometer 84and a fixed resistor 86 to a DC integrator 88, more specifically to itsfirst input 88a. The integrator has a second input 88b and an output88c. The input 88b is connected through a resistor 90 to ground so thata zero or common potential is applied to the input 88b. The DCintegrator 88 can be a conventional operational amplifier, theintegrating capabilities of which are well known when a feedbackcapacitor, such as that shown at 92, is employed. As is customary also,operational amplifiers invert the polarity of an input signal so thatthe output signal if of opposite polarity. This should be kept in mindduring the ensuing description.

Connected to the output 88c of the integrator 88 is a resistor 94, theother end of which is connected to a zero crossing comparator 96, alsoan operational amplifier. The comparator 96 has a pair of inputs 96a and96b plus an output labeled 96c. The output 96c is connected to aresistor 98 which in turn is connected to the gate of a field effecttransistor 100 which functions as a first switch device to apply acertain potential (actually zero) to the inputs 52b, 54b when closed,"as will be better understood as the description progresses. The drain ofthe transistor 100 is connected directly to the input 96b of the zerocrossing comparator 96. Both the input 96b and the drain of thetransistor 100 are connected to ground. The source of the transistor 100is connected to the inputs 52b and 54b of the multipliers 52, 54.

It will be helpful to explain what takes place according to specifictime intervals. At this stage of the description, it can be pointed outthat the initial time period is represented by the period from I, to tas far as the signal 70 of FIG.3 is concerned. This period is anindefinite period, being really a stop condition period. In other words,the contacts 74 and 76 are in the condition or position that they appearin in FIG. 1. During the time t, to t the output of the integrator 88 issaturated and clamped to a negative level because the input signal is apositive voltage through the normally closed contacts 74. Morespecifically, the electrical path can be traced from positive supplyvoltage V*, the resistor 80, the contacts 74, the potentiometer 84, thefixed resistor 86 to the input 88a of the integrator 88. Whereas theinput 88a has a positive voltage applied thereto, owing to the inversionof polarity by the integrator 8 8 the output is negative. The clampingaction, however, is derived through the agency of a diode 99 havings itsanode connected to ground and its cathode connected to the previouslymentioned resistor 94. A resistor llll is connected in parallel with thediode99. In other words, the forward bias of the diode 99 supplies thenegative clamping action, more specifically 0.6 volts.

An effort has been made to show this clamping voltage in FIG. 3.

The above action results in the same negative clamping voltage levelbeing applied to the input 96a of the zero crossing comparator 96. Owingto the polarity inversion taking place in the comparator 96, the outputof this comparator is saturated at a positive voltage. The positivevoltage is applied to the gate of the transistor 100 through thepreviously referred to resistor 98, thereby turning on the transistor100. Inasmuch as the drain of the transistor 100 is connected to ground,this applies a zero potential to the inputs 52a and 54a of themultipliers 52, 54. This zero voltage appears as e in FIG. 3 andprevails during the initial period t,,.'- t With the input signalimpressed on the input 52b and the input 54b equal to zero volts, thenit follows that the multiplication thereof with the full scaleoscillatory signal 68 supplied by the function generator 56 or bothgenerators 56 and 58 will produce a zero voltage output signal at theoutputs 52c and 54c of the multipliers 52 and 54. Hence, no signal isdelivered to the input terminals 28a of the comparators 28. Thereforethe testing apparatus 10 remains inactive and no vibration is applied tothe specimen 12 by the actuators l6, 18.

On the other hand, when the switch positions are reversed as far as thecontacts 74 and 76 are concerned, then the contacts 74 are open and thecontacts 76 closed. Graphically, this is from at t in FIG. 3. The smallamount of time from t to t, is required to bring the output signal fromthe integrator 88 from its negative clamped voltage to zero voltage. Itis at time t that the input signal to the integrator 88 changes polarityby reason of the closure of the contacts 76 which applies a negativevoltage from the negative supply V, doing so through the resistor 82. Itwill be understood that this causes the output signal from theintegrator 88, that is the signal appearing at the output terminal 88c,to ramp from its negative value with a positive slope. This rise periodis extremely small because the integra tor 88 is ramping at a very fastrate. In this regard, it will be appreciated that the voltage identifiedas V, at

6 the junction labeled 102 is virtually equal to tive supply voltage V,as explained abio'v time, though, the amplitude controlledrate I 7remains at zero as is evident from FIG. 2, thlshmg 59 because the fieldeffect transistor 100 is still on, which in effect, connects the inputs52d 5 ground owing to the switching function performed thereby. M Thenext period of time is from i, to i as fai as the signal is concerned.This is defined as the tl'ii'n on period when the output signal fromtheinte'gra'tor reaches zero volts, the output si na from trig erscrossing comparator 96, that is the signal at its tiutpiit 96c, willchange state from positive saturation tonega; tive satntation. Thisresults in switching out the field effect transistor I00. v At thistime, attention is called to a resistor 101i nected to the junction 1'02and the collector, of P P transistor 106. The emittei' of the transistor166 is eon; nected to ground, whereas the base of this transistol' isconnected throirgh a resistoi' 108 to the pro iofnsli mentioned resistorhaving one end thereof nected to the gate of the field effect transistofwhich acts as a second switch device. Up to this point,

the transistor 106 remains in a nonconductive or off condition. k r Asecond field effect transistor 110 has its drain nected to the resistor94 extending from the output of the integrator 88. The source of thefield effect transistor 110, however, is connected directly to theinputs 52b and 54b of the multipliers 52 and 54. Before exmorning theswitching action that involves mo field effect transistors 10.0 and 110,it will be well to describe the biasing arrangement for the transistor110. Acc'oid ingly, there is adiode 112 having its anode connected tothe output 96c of the zero crossing comparator 96. The cathode of thediode 112 has one end of a resistor 114 connected thereto, the other endof the resistor 114 being connected to the base of the NPN transistor116, the collector of which is connected through a resistor 117 to thepositive supply voltage V and the emitter thereof beingconnected througharesistor to the negative supply voltage V. A base resistor 119 extendsalso to the negative supply voltage V. Consequently, when the zerocrossing comparatoi' changes state from positive saturation to negativesaturation the field effect transistor is switched outan'd thetransistor switched in. In this regard, it will be observed that theoutput 960 is connected tothe base of the transistor 116 and theincrease of the base bias in a positive direction causes the transistor116 to be turned off. This raises the potential in a positive directionthat is applied to the gate of the field effect transistor 110 so thatthe transistor 110 is switched on.

Also, during this interval, the integrating rate of the integrator 88 isdecreased, this being accomplished by decreasing the input voltage atjunction 102. With the base bias applied through the resistorlOSunderthese I conditions being of negative polarity, it follows thatthe PNP transistor 106 is turned on However, by rendering the junction102 less negative than before the transistor 106 is made conductiveresults in a less negative voltage being applied to the input 88a of theintegrator 88. This accounts for a decrease in the integrating rate. Theamplitude controlled rate signal 70 signal at the output 88c of theintegrator 88 and inasmuch as the field effect transistor 110 isswitched on at this time,

the signal is impressed on the two input terminals 52!: and 54b of themultipliers 52, 54. The multiplication taking place between the signalat the input terminals 52b, 54b and the oscillatory signal applied tothe inputs 52a and 54a results in an output signal that is increasing asfar as its peak-to-peak amplitude is concerned. The portion of theresulting output signal 72 that is provided by the positive-going rampor during this time interval from t, to r, provides a positive rampvoltage indicated by e,. This is derived from the output rise voltage ehas been indicated by the numeral 72a. Consequently, the portion 72a isimpressed onto the inputs 28a of the comparators 28 and through theservovalves 20, 22 such a signal is delivered to the testing actuators16, 18. In this way, a moderated vibratory load is applied to thespecimen 12, being less than that which would be produced by thepeak-to-peak amplitude of the signal 70 delivered by the functiongenerator 56 or the generators 56, 58.

It is from the time t, to t, that the output signal 72 equals the fullscale command. More specifically, this time portion of the signal hasbeen indicated by the reference numeral 72b. This time interval isactually programmed by a master amplitude control labeled 120 whichcontains a potentiometer 122 having an adjustable wiper arm 123. Bysetting the wiper arm 123 the magnitude of a voltage applied to theinput 124a of an amplitude comparator 124 can be adjusted. The amplitudecomparator 124 is another operational amplifier, possessing theinversion capabilities of those already referred to herein. It has asecond input l24b and an output l24c. The output 124:: is connected tothe gate of a third field effect transistor 126 through a resistor 128.It will be appreciated that the transistor 126 functions as stillanother switch device. The drain of this transistor 126 is connected tothe wiper arm 123 of the potentiometer 122 and also to the input 124a ofthe comparator 124. The source, however, of the field effect transistor126 is connected to the inputs 52b, 54b of the multipliers 52 and 54.

In addition to being attached to the resistor 128, the output l24c ofthe amplitude comparator 124 is connected to the anode of a diode 130,the cathode thereof being connected to the cathode of the previouslymentioned diode 112 and the end of the resistor 114 that is attached tothe cathode of the diode 112.

Consequently during the period extending from t, to the output signalfrom the amplitude comparator 124 is instrumental in switching the thirdfield effect transistor 126 in and the second field effect transistor110 out. The output from the integrator 88 continues to ramp towardpositive saturation during this period. However, the amplitudecontrolled rate signal 70 during this interval equals the voltagesupplied by the master amplitude control 120. This voltage in FIG. 3 hasbeen denoted by the reference character a Owing to the fact that thefield effect transistor 110 has been switched out of the circuit, it isinefiectual as far as applying the output from the integrator 88 toeither of the inputs 52b, 54b of the multipliers 52 and 54. The onlysignal that is applied to the inputs 52b and 54b at this time is throughthe third field effect transistor 126 which, as mentioned above, isapplying the voltage provided by the positioning of the wiper arm 123 ofthe potentiometer 122, the potentiometer 122 actually constituting themaster amplitude control denoted by the numeral 120.

It will be appreciated that the period extending from I, to 1;, is anindefinite one, depending upon the length of test as far as the specimen12 is concerned. To term-inate the testing operation, the togglemechanism 78 associated with the contacts 74 and 76 is moved back to itsstop position, thereby returning the contacts 74 to their normallyclosed position and the contacts 76 to their open position. Thisreverses the polarity applied to the input 88a of the integrator 88, forthe closed contacts 74 apply a positive voltage derived from thepositive supply voltage V*. This causes the output signal from theintegrator 88 to ramp with a negative slope. Whereas previously therewas a rise to the output, it now is falling. This amount of time fromr;, to z, is quite small because the integrator 88 is ramping at agreater rate than during the turn on period from t, to 1 and also at agreater rate than the turn off period which has not yet been referred tobut which is from I to t The section of the circuitry causing the fasterramping rate includes a junction 132 having a voltage V,. The junction132 is connected to one end of a resistor 134 and the other end of thisresistor is connected to the collector of a NPN transistor 136. Theemitter of the transistor 136 is connected directly to ground, whereasthe base thereof is connected through a resistor 138 to the collector ofthe previously mentioned transistor 116 and also to the gate resistorlll associated with the second field effect transistor 110. Due to thefact that the transistor 136 is off or nonconductive at this time, itwill 'be appreciated that the voltage V is equal to the positive supplyvoltage V*. The amplitude controlled rate signal during this period fromt;, to t still equals the voltage supplied from the master amplitudecontrol 120.

Passing now to the period t to it will be recognized that this is theturn off period, because the dynamic command is decreasing at a linearrate during this interval. Consequently, when the output signal from theintegrator 88 equals the master amplitude voltage 2 the output signalfrom the amplitude comparator 124 changes state. This results inswitching in the second field effect transistor and switching out thethird field effect transistor 126. It will be recognized that thetransistor 110, being switched on, then applies the output signal fromthe integrator 88 to the inputs 52b and 54b of the multipliers 52 and54.

It should be pointed out, though, that the integrating rate of theintegrator 88 is decreased at the time t by decreasing the input voltageV, at the junction 132. This is the responsibility of the transistor136, for by turning on the transistor 136 the voltage V at the junction132 is decreased. In this regard, when the amplitude comparator 124changes state as far as its output 124a is concerned, then at the sametime that the field effect transistor 126 is switched out of thecircuit, the bias applied to the base of the transistor 136 is increasedin a positive direction to cause conduction of this transistor. This isdeveloped from the fact that the transistor 116 is turned off by thereversal of polarity as far as the output signal from the amplitudecomparator 124 is concerned. At any rate, it should be obvious that theamplitude controlled rate signal 70 during the time interval from t toprovides a negative ramp labeled e, from the output of the integrator 88to produce the portion 72 c of the signal 72. The falling rate duringthe turn off period can be considerably faster than the turning on rate,and this is taken advantage of by means trolled rate signal equals zerovolts as can be discerned from the right hand portion of the signal 70presented in FIG. 3. What occurs is that the output from the integrator88 falls to zero volts and this causes the zero crossing comparator 124to switch in the first field effect transistor 100 and switch out thesecond field effect transistor 110. The output signal from theintegrator 88 continues to ramp or fall to a negative 0.6 volts due tothe clamping action of the diode 99 as already explained. The amplitudecontrolled rate signal 70 will remain at its zero level until the togglemechanism 78 is again actuated so as to open the contacts 74 and toclose the contacts 76. This would cause a repetition of what has alreadybeen described in the way of operatron.

From the foregoing, the operation of my system has actually already beengiven in sufficient detail to make it understandable. It should beappreciated, though, that the system provides a linear controlled ratein contradistinction to previous approaches utilizing a-nonlinear rate.As already pointed out, the nonlinear rate results in an unpredictablenumber of cycles being required to obtain a precision peak-to-peakamplitude. The integrator 88, it will be seen, does not remain in thecircuit during the actual application of the full scale command signal.Instead, the integrator 88 is employed only during the turn on and turnoff portions of the testing sequence, the integrator being switched outof the circuit during the remainder of the time by virtue of theswitching out of the field effect transistor 110. All of the switchingis done electronically by the field efiect transistors 100, 110 and 126to provide a smooth transistion from the ramp portions of the signal 70,both as to the rise and fall thereof. This additionally contributes tothe accuracy of the static level involving the portion 72b of theresulting output command signal 72.

Recapitulating, the signals 68 and 70 are multiplied together to producethe signal 72. Inasmuch as the wave forms presented in FIGS. 2-4 wereprepared by a strip chart recorder, in order to avoid anymisunderstanding as to the amplitude of the product signal 72 appearingin H0. 4 it should be explained that the Motorola multipliers 52 and 54automatically divide by a constant factor of 10, thereby providing aproduct signal 72 only one-tenth the scale that would otherwise exist.Whether the factor is one, ten or any other number is unimportant to theinvention, depending instead on practical considerations not hereininvolved.

Assuming that the function generators 56 and 58 provide differentoscillatory signals, although the signal 68 may be regarded asexemplary, both of the switches 60 and 64 would be closed, whereas theswitch 62 would be open. This would apply different signals to theinputs 52a and 540. However, master amplitude control 120 then serves toapply the same signal 70 to both inputs 52b and 54b of the multipliers52 and 54. Thus, the full scale oscillatory signals supplied by thefunction generators 56 and 58 will be effective as far as the vibrationapplied to the specimen 12 by the two actuators 16 and 18. Yet, only onemaster amplitude control 120 is used and also only one amplitudecontrolled rate circuit 66 is needed.

The function generator 56 by closing the switches 60 and 62, and openingthe switch 64, can be caused to supply both of the inputs 52a and 54awith the functiongenerator signal 68. This will result in the actuators16 and I8 applying the same type of vibration to the specimensat the twospaced locations.

While two channels have been alluded to, it will be appreciated that anynumber of channels can be controlled by a single master amplitudecontrol I20.

I claim:

l. A system for controlling the turn on rate of an oscillatory s ign glfor a test apparatus including a fe'eipro catlng actuator wfi'fitted toa tittiiiittiftmtftis rneans for supplying an oscillatory signaTto saidactuator, the turn on rate of which is 'to be controlled to preventdamagin'g'the specimen, means providing a ramp signal having a slopeportion, and means for multiplying said signals together to provide anoscillatory out put signal increasing in peak-to-peak amplitude inaccordance with the rate of rise of said slope portion during a desiredturn on time, means providing a steady state reference signal to saidmultiplying means when the ramp signal reaches a preselected value, andswitch means to connect the multiplying means to the last mentionedmeans when the ramp portion reaches said preselected value.

2. The system as defined in claim 1 in which said ramp signal means alsoprovides a second slope portion for controlling the turn off rate ofsaid output signal, and means to disconnect the reference signal meansfrom the multiplier and to connect said second slope portion of rampsignal means to said multiplying means when said means providing thereference signal is disconnected from said multiplying means.

3. The system as defined in claim 2 in which said first slope portionincreases at a linear rate.

4. The system as defined in claim 3 in which said sec ond slope portiondecreases at a linear rate different rom said first slope portion.

5. The system as defined in claim 4 including means for adjusting themagnitude of said reference signal.

The system as defined in claim 5 including vibration testing apparatusconnected to the output of said multiplying means so that saidoscillatory output signal controls said apparatus.

7. A system for controlling the turn on rate of an oscillatory signalcomprising means for supplying an oscillatory signal, the turn on rateof which is to be con trolled, a multiplier having first and secondinputs and an output, said signal supplying means being connected tosaid first input, first switch means connected to said second input forapplying a zero potential signal thereto so that the product signal atsaid output is zero when said switch means is closed, an integrator forproviding a positive slope signal during a given interval of time,second switch means connected between'the output of said integrator andsaid second input, means for applying a signal to said integrator tocause said integrator to supply said positive slope signal, saidlastmentioned means opening said first'switch means and closing saidsecond switch means to apply said positive slope signal through saidsecond switch means to said second input, and means for opening saidsecond switch means when said positive slope signal reaches apredetermined magnitude and then applying a signal of said predeterminedmagnitude to the second input of said multiplier.

8. The system as defined in claim 7 including a constant potentialsource for applying said predetermined magnitude signal.

9. The system as defined in claim 8 in which said source is apotentiometer.

10. The system as defined in claim 9 including vibration testingapparatus connected to the output of said multiplier so that saidproduct signal is supplied to said testing apparatus during the intervalwhen said positive slope signal is increasing and also during thesucceeding interval when said constant potential signal is applied tosaid second input.

11. The system as defined in claim 7 in which said last-mentioned meansincludes a third switch means and a potentiometer for supplying aconstant potential signal through said third switch means to said secondinput when said third switch means is closed, said lastmentioned meansfurther including means for closing said third switch means when saidpositive slope signal reaches said predetermined magnitude.

12. The system as defined in claim 11 including vibration testingapparatus connected to the output of said multiplier so that saidproduct signal is supplied to said testing apparatus.

13. The system as defined in claim 12 including means for causing saidintegrator to provide a negative slope signal, and means for causingsaid second switch means to close and said third switch means to open sothat said negative slope signal is applied to said second input.

14. The system as defined in claim 13 including means for reclosing saidfirst switch means and reopening said second switch means to again applysaid zero potential signal to said second input.

15. The system as defined in claim 14 in which said vibration apparatusincludes a pair of channels, one channel being supplied by theoscillatory output signal from the output of said first multiplier, asecond multiplier having first and second inputs and an output, meansfor connecting said oscillatory signal supplying means to the firstinput of said second multiplier, means for connecting said first switchmeans to the second output of said second multiplier, the other of saidpair of channels being connected to the output of said secondmultiplier.

16. The system as defined in claim 15 including additional means forsupplying a second oscillatory signal, a first switch for connectingsaid additional means to the first input of said second multiplier, saidmeans for connecting said oscillatory signal supplying means to thefirst input of said second multiplier including a second switch.

17. The system as defined in claim 16 including a third switch betweensaid first oscillatory signal supplying means and the first input ofsaid first multiplier.

18. A system for controlling the turn on rate of an oscillatory signalcomprising a function generator for supplying an oscillatory signal, amultiplier having first and second inputs and an output, said firstinput being connected to said function generator, an integrator havingan input and an output, means for connecting the input of saidintegrator to a voltage having one polarity, means for connecting theoutput of said integrator to the second input of said multiplier duringone time period, means for disconnecting the output of said integratorfrom the second input of said multiplier during a second time period,and means for connecting a steady state signal to the second input ofsaid multiplier during said second time period.

19. The system as defined in claim 18 including means for reconnectingthe output of said integrator to the second input of said multiplierduring a third time period, means for reversing the polarity of saidvoltage applied to the input of said integrator during said third timeperiod, and means for disconnecting said steady state signal from thesecond input of said multiplier during said third time period, wherebythe turn off rate of said oscillatory signal supplied by said functiongenerator is also controlled.

20. The system as defined in claim 19 including vibration testingapparatus connected to the output of said multiplier so that theoscillatory signal from said function generator, which is supplied tosaid vibration testing apparatus from the output of said multiplier, isapplied to said vibration apparatus at an increasing peak-to-peak rateduring said first time period and removed from said vibration apparatusat a decreasing peak-to-peak rate during said third time period.

21. A system for controlling the turn on and turn off rate of anoscillatory signal used for testing including a reciprocating testingapparatus, said testing apparatus including a plurality of channels,first means for supplying a first oscillatory signal, second means forsupplying a second oscillatory signal, means providing a ramp signalhaving a first slope portion having a rate of magnitude increase, asecond slope portion having a rate of magnitude decrease and anintermediate portion of substantially constant magnitude, firstmultiplying means for multiplying said first oscillatory signal and saidramp signal together to give a first output signal which has a peak topeak amplitude that varies as a function of said ramp signal, secondmultiplying means for multiplying said second oscillatory signal andsaid ramp signal together to deliver a second output signal which has apeak to peak amplitude that varies as a function of said ramp signal,and means connecting said first output signal to a first of saidchannels and said second output signal to a second of said channels.

22. The system as defined in claim 21 including means for connectingsaid first oscillatory signal supplying means to said second multiplyingmeans in addition to being connected to said first multiplying means,and means for disconnecting said second oscillatory signal supplyingmeans from said second multiplying means so that said first oscillatorysignal supplying means supplies the same oscillatory signal to bothmultiplying means.

23. A command signal system for controlling the rate of increase of afirst oscillatory command signal when said first command signal isinitially supplied to a controlled device including a reciprocatingactuator connected to a specimen comprising means for supplying a firstoscillatory command signal to the actuator, means providing a secondramp command signal independent of the controlled device and having aramp portion increasing at a selected ramp rate from a first levelduring a desired turn on time for said actuator, means for combiningsaid signals and delivering a command output signal which has a rate ofincrease during said turn on time which is a function of the second rampcommand signal, and means to provide a reference signal, switch means todisconnect the second ramp signal from the combining means and toconnect the reference signal to the combining means when the ramp signalreaches a preselected level so that subsequent to the turn on time thecommand output signal varies as a function of the first command outputsignal and the reference signal.

24. The combination of claim 23 and control means for disabling saidcommand output signal, said means providing said second ramp commandsignal including means providing a decreasing rate ramp signal portiondecreasing from the reference level to said first level when the controlmeans for disabling said command output signal is actuated.

25. A system for controlling the turn on and turn off rate of a signalcontrolling a loading apparatus comprising a multiplier having first andsecond inputs and an output, a function generator for applying arelatively constant peak-to-peak oscillatory signal to the first inputof said multiplier, and an amplitude controlled rate circuit independentof the load applied by the loading apparatus for applying a ramp-typesignal to the second input of said multiplier, said amplitude controlledrate circuit including a direct current integrator having first andsecond inputs and an output, said integrator inverting the polarity ofan input signal so that the output signal is of opposite polarity andthe second input thereof being connected to a zero reference potential,means for first applying a positive potential to the first input of saidintegrator, means clamping the output of said integrator to a negativepotential while said positive potential is applied to the first input ofsaid integrator, a zero crossing comparator having first and secondinputs and an output, said zero crossing comparator inverting thepolarity of an input signal so that the output signal is of oppositepolarity and said clamping means also applying said negative potentialto the first input of said zero crossing comparator and said secondinput of said zero crossing comparator being connected to said zeroreference potential, a first field effect transistor having its gateconnected to the output of said zero crossing comparator, its drainconnected to said zero reference potential and its supply to the secondinput of said multiplier so that a positive potential is initiallyapplied to the gate of said field effect transistor to turn on saidfield effect transistor and thereby apply said zero reference potentialto the second input of said multiplier with the consequence that theproduct signal supplied at the output of said multiplier is zero, meansfor reversing the polarity applied to the first input of said integratorto a negative potential to provide a positive ramp potential to theoutput of said integrator to cause the signal at the output thereof tochange to a negative potential to switch out said first field effecttransistor, a second field effect transistor having its drain connectedto the output of said integrator and its supply connected to the secondinput of said multiplier, means responsive to the means for applying anegative potential to the first input of said integrator to apply apositive potential to the gate of said second field effect transistor toturn on said second field effect transistor and thereby apply saidpositive ramp potential from said integrator to the second input of saidmultiplier, an amplitude comparator having first and second inputs andan output, said amplitude comparator inverting the polarity of an inputsignal so that the output signal is of opposite polarity, meansproviding a constant positive potential, the first input of saidamplitude comparator being connected to said constant positive potentialand the second input thereof being connected to the output of saidintegrator, a third field effect transistor having its gate connected tothe output of said amplitude comparator, its drain to said constantpositive potential means and its supply to the second input of saidmultiplier so that the positive ramp potential from said integrator isapplied to the second input of said amplitude comparator to provide apositive signal from the output of said amplitude comparator to the gateof said third field effect transistor to thus turn on said third fieldeffect transistor and thereby apply said constant positive potentialfrom said constant positive potential means to the second input of saidmultiplier, means connected to the output of said amplitude comparatorfor turning ofi said second field effect transistor, means for againapplying said positive potential to the first input of said integratorto cause said integrator to ramp with a negative slope, and meansresponsive to said last-mentioned means for turning off said third fieldeffect transistor and turning said second field effect transistor.

26. The system as defined in claim 30 in which said constant positivepotential means includes a potentiometer.

1. A system for controlling the turn on rate of an oscillatory signalfor a test apparatus including a reciprocating actuator connected to aspecimen, comprising means for supplying an oscillatory signal to saidactuator, the turn on rate of which is to be controlled to preventdamaging the specimen, means providing a ramp signal having a slopeportion, and means for multiplying said signals together to provide anoscillatory output signal increasing in peak-to-peak amplitude inaccordance with the rate of rise of said slope portion during a desiredturn on time, means providing a steady state reference signal to saidmultiplying means when the ramp signal reaches a preselected value, andswitch means to connect the multiplying means to the last mentionedmeans when the ramp portion reaches said preselected value.
 2. Thesystem as defined in claim 1 in which said ramp signal means alsoprovides a second slope portion for controlling the turn off rate ofsaid output signal, and means to disconnect the reference signal meansfrom the multiplier and to connect said second slope portion of rampsignal means to said multiplying means when said means providing thereference signal is disconnected from said multiplying means.
 3. Thesystem as defined in claim 2 in which said first slope portion increasesat a linear rate.
 4. The system as defined in claim 3 in which saidsecond slope portion decreases at a linear rate different rom said firstslope portion.
 5. The system as defined in claim 4 including means fOradjusting the magnitude of said reference signal.
 6. The system asdefined in claim 5 including vibration testing apparatus connected tothe output of said multiplying means so that said oscillatory outputsignal controls said apparatus.
 7. A system for controlling the turn onrate of an oscillatory signal comprising means for supplying anoscillatory signal, the turn on rate of which is to be controlled, amultiplier having first and second inputs and an output, said signalsupplying means being connected to said first input, first switch meansconnected to said second input for applying a zero potential signalthereto so that the product signal at said output is zero when saidswitch means is closed, an integrator for providing a positive slopesignal during a given interval of time, second switch means connectedbetween the output of said integrator and said second input, means forapplying a signal to said integrator to cause said integrator to supplysaid positive slope signal, said last-mentioned means opening said firstswitch means and closing said second switch means to apply said positiveslope signal through said second switch means to said second input, andmeans for opening said second switch means when said positive slopesignal reaches a predetermined magnitude and then applying a signal ofsaid predetermined magnitude to the second input of said multiplier. 8.The system as defined in claim 7 including a constant potential sourcefor applying said predetermined magnitude signal.
 9. The system asdefined in claim 8 in which said source is a potentiometer.
 10. Thesystem as defined in claim 9 including vibration testing apparatusconnected to the output of said multiplier so that said product signalis supplied to said testing apparatus during the interval when saidpositive slope signal is increasing and also during the succeedinginterval when said constant potential signal is applied to said secondinput.
 11. The system as defined in claim 7 in which said last-mentionedmeans includes a third switch means and a potentiometer for supplying aconstant potential signal through said third switch means to said secondinput when said third switch means is closed, said last-mentioned meansfurther including means for closing said third switch means when saidpositive slope signal reaches said predetermined magnitude.
 12. Thesystem as defined in claim 11 including vibration testing apparatusconnected to the output of said multiplier so that said product signalis supplied to said testing apparatus.
 13. The system as defined inclaim 12 including means for causing said integrator to provide anegative slope signal, and means for causing said second switch means toclose and said third switch means to open so that said negative slopesignal is applied to said second input.
 14. The system as defined inclaim 13 including means for reclosing said first switch means andreopening said second switch means to again apply said zero potentialsignal to said second input.
 15. The system as defined in claim 14 inwhich said vibration apparatus includes a pair of channels, one channelbeing supplied by the oscillatory output signal from the output of saidfirst multiplier, a second multiplier having first and second inputs andan output, means for connecting said oscillatory signal supplying meansto the first input of said second multiplier, means for connecting saidfirst switch means to the second output of said second multiplier, theother of said pair of channels being connected to the output of saidsecond multiplier.
 16. The system as defined in claim 15 includingadditional means for supplying a second oscillatory signal, a firstswitch for connecting said additional means to the first input of saidsecond multiplier, said means for connecting said oscillatory signalsupplying means to the first input of said second multiplier including asecond switch.
 17. The system as defined in claim 16 including a thirdswitch between said first oscillatory signal supplying means and thefirst input of said first multiplier.
 18. A system for controlling theturn on rate of an oscillatory signal comprising a function generatorfor supplying an oscillatory signal, a multiplier having first andsecond inputs and an output, said first input being connected to saidfunction generator, an integrator having an input and an output, meansfor connecting the input of said integrator to a voltage having onepolarity, means for connecting the output of said integrator to thesecond input of said multiplier during one time period, means fordisconnecting the output of said integrator from the second input ofsaid multiplier during a second time period, and means for connecting asteady state signal to the second input of said multiplier during saidsecond time period.
 19. The system as defined in claim 18 includingmeans for reconnecting the output of said integrator to the second inputof said multiplier during a third time period, means for reversing thepolarity of said voltage applied to the input of said integrator duringsaid third time period, and means for disconnecting said steady statesignal from the second input of said multiplier during said third timeperiod, whereby the turn off rate of said oscillatory signal supplied bysaid function generator is also controlled.
 20. The system as defined inclaim 19 including vibration testing apparatus connected to the outputof said multiplier so that the oscillatory signal from said functiongenerator, which is supplied to said vibration testing apparatus fromthe output of said multiplier, is applied to said vibration apparatus atan increasing peak-to-peak rate during said first time period andremoved from said vibration apparatus at a decreasing peak-to-peak rateduring said third time period.
 21. A system for controlling the turn onand turn off rate of an oscillatory signal used for testing including areciprocating testing apparatus, said testing apparatus including aplurality of channels, first means for supplying a first oscillatorysignal, second means for supplying a second oscillatory signal, meansproviding a ramp signal having a first slope portion having a rate ofmagnitude increase, a second slope portion having a rate of magnitudedecrease and an intermediate portion of substantially constantmagnitude, first multiplying means for multiplying said firstoscillatory signal and said ramp signal together to give a first outputsignal which has a peak to peak amplitude that varies as a function ofsaid ramp signal, second multiplying means for multiplying said secondoscillatory signal and said ramp signal together to deliver a secondoutput signal which has a peak to peak amplitude that varies as afunction of said ramp signal, and means connecting said first outputsignal to a first of said channels and said second output signal to asecond of said channels.
 22. The system as defined in claim 21 includingmeans for connecting said first oscillatory signal supplying means tosaid second multiplying means in addition to being connected to saidfirst multiplying means, and means for disconnecting said secondoscillatory signal supplying means from said second multiplying means sothat said first oscillatory signal supplying means supplies the sameoscillatory signal to both multiplying means.
 23. A command signalsystem for controlling the rate of increase of a first oscillatorycommand signal when said first command signal is initially supplied to acontrolled device including a reciprocating actuator connected to aspecimen comprising means for supplying a first oscillatory commandsignal to the actuator, means providing a second ramp command signalindependent of the controlled device and having a ramp portionincreasing at a selected ramp rate from a first level during a desiredturn on time for said actuator, means for combining said signals anddelivering a command output signal which has a rate of increase duringsaid turn on time wHich is a function of the second ramp command signal,and means to provide a reference signal, switch means to disconnect thesecond ramp signal from the combining means and to connect the referencesignal to the combining means when the ramp signal reaches a preselectedlevel so that subsequent to the turn on time the command output signalvaries as a function of the first command output signal and thereference signal.
 24. The combination of claim 23 and control means fordisabling said command output signal, said means providing said secondramp command signal including means providing a decreasing rate rampsignal portion decreasing from the reference level to said first levelwhen the control means for disabling said command output signal isactuated.
 25. A system for controlling the turn on and turn off rate ofa signal controlling a loading apparatus comprising a multiplier havingfirst and second inputs and an output, a function generator for applyinga relatively constant peak-to-peak oscillatory signal to the first inputof said multiplier, and an amplitude controlled rate circuit independentof the load applied by the loading apparatus for applying a ramp-typesignal to the second input of said multiplier, said amplitude controlledrate circuit including a direct current integrator having first andsecond inputs and an output, said integrator inverting the polarity ofan input signal so that the output signal is of opposite polarity andthe second input thereof being connected to a zero reference potential,means for first applying a positive potential to the first input of saidintegrator, means clamping the output of said integrator to a negativepotential while said positive potential is applied to the first input ofsaid integrator, a zero crossing comparator having first and secondinputs and an output, said zero crossing comparator inverting thepolarity of an input signal so that the output signal is of oppositepolarity and said clamping means also applying said negative potentialto the first input of said zero crossing comparator and said secondinput of said zero crossing comparator being connected to said zeroreference potential, a first field effect transistor having its gateconnected to the output of said zero crossing comparator, its drainconnected to said zero reference potential and its supply to the secondinput of said multiplier so that a positive potential is initiallyapplied to the gate of said field effect transistor to turn on saidfield effect transistor and thereby apply said zero reference potentialto the second input of said multiplier with the consequence that theproduct signal supplied at the output of said multiplier is zero, meansfor reversing the polarity applied to the first input of said integratorto a negative potential to provide a positive ramp potential to theoutput of said integrator to cause the signal at the output thereof tochange to a negative potential to switch out said first field effecttransistor, a second field effect transistor having its drain connectedto the output of said integrator and its supply connected to the secondinput of said multiplier, means responsive to the means for applying anegative potential to the first input of said integrator to apply apositive potential to the gate of said second field effect transistor toturn on said second field effect transistor and thereby apply saidpositive ramp potential from said integrator to the second input of saidmultiplier, an amplitude comparator having first and second inputs andan output, said amplitude comparator inverting the polarity of an inputsignal so that the output signal is of opposite polarity, meansproviding a constant positive potential, the first input of saidamplitude comparator being connected to said constant positive potentialand the second input thereof being connected to the output of saidintegrator, a third field effect transistor having its gate connected tothe output of said amplitude comparator, its dRain to said constantpositive potential means and its supply to the second input of saidmultiplier so that the positive ramp potential from said integrator isapplied to the second input of said amplitude comparator to provide apositive signal from the output of said amplitude comparator to the gateof said third field effect transistor to thus turn on said third fieldeffect transistor and thereby apply said constant positive potentialfrom said constant positive potential means to the second input of saidmultiplier, means connected to the output of said amplitude comparatorfor turning off said second field effect transistor, means for againapplying said positive potential to the first input of said integratorto cause said integrator to ramp with a negative slope, and meansresponsive to said last-mentioned means for turning off said third fieldeffect transistor and turning said second field effect transistor. 26.The system as defined in claim 30 in which said constant positivepotential means includes a potentiometer.